This application claims priority of German Patent Application No. 10150786.0, filed Oct. 15, 2001, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method and an apparatus for the automatic setting of injectors, in particular a method and an apparatus for the automatic setting of fuel or diesel injectors in the course of the production of the injectors in a production line, each injector including a piezoelectric actuator, a straight-through valve, a lever element coupled to the straight-through valve and a setting element coupled to the piezoelectric actuator.
2. Related Art
The production of modern diesel injectors is currently normally carried out by way of a two-stage production process. In a first process, the individual components of the diesel injectors are assembled within the context of preassembly and, for example, screwed to one another. In a second process, the preassembled diesel injector is set so as to be serviceable, that is to say the injector is adjusted in such a way that firstly it has the longest possible lifetime and secondly it makes a contribution to achieving the lowest possible fuel consumption. Modern diesel injectors operate with a so-called piezoelectric actuator, which is coupled to a straight-through valve via a lever element, so that by applying a suitable electrical voltage to the piezoelectric actuator, the opening of closing of the straight-through valve can be controlled. In order to optimize the lifetime of the diesel injector and the injection behaviour of the diesel injector, the physical position of the piezoelectric actuator relative to the lever element must be set as accurately as possible. In particular in the case of diesel injectors which permit multiple injection, the distance between the piezoelectric actuator and the lever element via which the straight-through valve is triggered must be set very precisely. In this connection, multiple injection is understood to mean switching through the injector repeatedly within a very short time interval, by the straight-through valve being opened and closed several times one after another.
For this reason, in modern diesel injectors the piezoelectric actuator can be displaced relative to the lever element by way of a setting element. In this way, adjustment of the piezoelectric actuator relative to the lever element can be achieved accurately down to a few micrometers. This adjustment, with which the injection behaviour of the diesel injector is set, is generally carried out manually at manual workstations.
One embodiment of the present invention provides a method and an apparatus for the automatic setting of injectors. That is, an injector preassembled on a production line being set so as to be serviceable.
The method according to the invention has the advantage that the injector setting may be carried out independently of an operator, so that the precision of the injector setting is increased. In particular in the case of the production of a large number of injectors, it is therefore possible to ensure that all the injectors are set largely identically. As a result of the use of a plurality of identically set injectors in a diesel engine having a plurality of cylinders, it is therefore possible for the overall engine behaviour to be improved.
According to an exemplary embodiment of the present invention, an injector set by way of the method of the present invention may be classified as correctly set when all the registered values agree with predefined parameters. Alternatively, the setting of the injector can also be checked by way of an injector test procedure, in which the piezoelectric actuator has a predetermined voltage/time profile applied to it. In this case, the injector set by way of the method of the present invention may be classified as correctly set when it switches through at a specific predefined voltage level. If the switching through action takes place at a different voltage level, the injector may be classified as incorrectly set. Therefore, a setting of the injector which is correct, that is to say has been carried out within a predefined tolerance, can be registered reliably.
According to another embodiment of the present invention, the setting procedure of the injector may be repeated if the injector has previously been classified as incorrectly set. This has the advantage that an initially incorrectly set injector does not have to be removed from the production process, but instead may be developed into a fully serviceable injector by way of a renewed correct setting. In this case, it may be practical to limit the number of setting procedures to be repeated. Depending on the size of the tolerance band for a correctly set injector, the maximum number of setting procedures to be carried out may, for example, lie between one and ten or even more. This ensures that, for example as a result of faulty preassembly of the injector to be set, the method according to the present invention is not carried out infinitely often, which would lead to a fault in the overall production sequence.
Additionally, according to the present invention, a correctly set injector may be removed from the measurement and setting station after the setting procedure. Thus, following the removal of the correctly set injector, a further injector preassembled on the production line can be provided in the correct position in the measurement and setting station by way of the handling apparatus.
This provides the possibility for a large number of preassembled injectors to be set correctly by way of setting procedures carried out one after another, and thus the productivity of the injector production can be increased significantly.
According to yet another embodiment of the present invention, the piezoelectric actuator has a specific sequence of charging pulses applied to it before the adjustment of the setting element. In this way, the reliability of the setting procedure can be increased considerably, since the characteristic expansion behaviour of the piezoelectric actuator when a specific electrical voltage is applied depends on the signals previously applied to the actuator. As a result of applying defined charging pulses to the piezoelectric actuator, the actuator is brought into a precisely defined state before the actual setting procedure. The precision of the injector setting can thus additionally be increased, so that in particular the number of setting procedures to be carried out again is reduced if the injector has previously been classified as incorrectly set.
Before the adjustment of the setting element, the injector is coupled to a high-pressure reservoir assuming a limited volume. As a result of the choice of a relatively small limited volume of, for example, 5 to 20 cm3, when the injector is switched through, a relatively large, significant pressure change is effected, which can be registered reliably by a manometer belonging to the pressure generating device.
According to a further preferred embodiment of the invention, during the adjustment of the setting element, the course of the torque applied to the setting element, the course of the angular position of the setting element, the course of the voltage applied to the actuator and/or the course of the pressure applied to the injector are registered. Registering the entire chronological course of the respective parameters has the advantage that, as compared with registering the parameters at a single time, more accurate assessment with regard to the correct setting of the injector can be performed.
The injector can additionally be fixed by way of a gripping apparatus, so that the risk of rotation of the injector during the adjustment of the setting element is reduced.
The apparatus according to an embodiment of the present invention may be achieved by an apparatus for the automatic setting of injectors having the features of claim 10.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.